Optical storage drives such as CD-ROM and DVD drives are well known in the art. An important element in such drives is the optical pickup unit (OPU). Typically, the OPU comprises laser light emitting diode, light detector, optical lens, and a voice coil. The voice coil is used to position the lens for proper focusing and tracking during a read/write operation. To be able to access different data tracks in an optical storage device, e.g., CD-ROM, the entire OPU has to move radially to the storage device on a linear sliding rail system. The OPU and the mechanism for positioning the OPU shall collectively be referred to as an optical pickup mechanism.
Some optical storage discs, e.g. laser discs and DVDs, have data stored on both sides. Therefore, some optical storage drives are equipped to access data from both sides of the disc. Currently, there are basically three different designs for accessing data from dual-sided discs. One way is to use a U-shape sliding rail system where a single OPU can move to either side of the disc. The second method is to employ two OPUs, one for each side of the disc. The third way is to manually flip the disc so the side to be accessed is facing the OPU.
All of these designs suffer from a number of shortcomings. First and foremost, all of the designs described above use a configuration where the entire OPU moves on a linear sliding rail system. Although this current configuration where the entire OPU moves on a linear sliding rail system has been used successfully for many years, it has its limitations, particularly in light of the current shorter data access time requirement. The OPU is a relatively bulky device which slows down the movement of the entire mechanism, and consequently, the time it takes to move from one track to a different track is increased. Although attempts have been made to increase the mobility of the OPU by applying more powerful motors, this has led to increased vibration, particularly in the voice coil which is most susceptible. Hence, the time saved from increased acceleration is offset by the time it takes to stabilize the unit before the accessed data can be read or written.
In addition, there are problems which are specific to each of the designs mentioned above. For the first design using a U-shaped rail, the system suffers from complexity and bulkiness, and hence takes up excessive amount of space and material. For the second design which uses the two OPUs, the main problem is cost, as OPU is an expensive component in an optical storage drive. For the third design, the main shortcoming is the inconvenience to the user who has to manually flip the disc.
To have a reliable and superior optical pickup mechanism which can read/write both sides of an optical storage disc, it must be capable of high acceleration without incurring vibrational problems. Moreover, it should be simple in design, convenient to the user, and inexpensive to manufacture. Since such a mechanism would greatly shorten the data access time of the current optical storage drives, save time and cost in manufacturing, and be attractive to the end users, it is easy to why such an optical pickup mechanism would be highly desirable and useful.